ScanFish… my experiences with the fascinating system!

ROTV ….the preface!

Plesseya Marine Systems Unit (PMSU) in 1970ies began development of an Undulating Tow Vehicle (UTV). The UTV had watertight electronic equipment capable of receiving and storing information from eight probes picking up various oceanographic data.

UOR (Undulating Oceanographic Recorder) MARK 1 came into existence in 2003. Its depth could be altered without having to change the length of the tow cable. The vehicle consists of three main structures consisting of the vehicle itself, cables and the towing winch.

UORs were classified in two categories: One with active depth control and other with fixed depth control.

The most common types of undulating towed vehicles are:

Batfish (Quildline Instruments (Canada)

NuShuttle and SeaSoar II (Chelsea Technologies Group, UK lately acquired by Sonardyne)

Scanfish (EIVA, Denmark)

There is in fact more to it but for now we’ll concentrate on the very popular ScanFish!

ScanFish as we know is quite a popular ROTV with hydrofoils that are controlled through a servomotor connected to a cable that attaches it to the vessel.

Connections and communication:

ScanFish setup uses Ethernet to communicate. SF IP address is always 10.10.103.XX, where XX is the last 2 digit of the Scanfish bottle serial number, engraved on the Starboard side of the bottle inside the Scanfish.

To find out the right IP address you can use the software “EivaHWConfig“. The ScanFish’s IP address starts always with 10.10.103.XXX and the last digits are specific for each SF.

For example, Port ScanFish (10.10.103.80) is controlled by EIVA Flight software through its TPU (10.10.103.235). Stbd SF (10.10.103.75) is controlled by its TPU (10.10.103.234). 

 The SF IP address had to be added in EIVA Flight \Settings \Options \Setup \Fish \ Fish connection.

For BIOS, place the Scanfish’s IP address (10.10.103.XXX) in a web browser. Information on the SF is available here and also changes to the settings can be made as in the Flight software plus few additional settings i.e. change the Ascending/ Descending Speed of the Scanfish (General Max Rate) to 1.2m/s. Default is 0.6m/s.

Payload ports on the ScanFish III with serial communication are connected to a Digi PortServer. To connect to these ports, virtual COM ports are installed on the host computer. Host computer is the computer connecting to the COM ports, not necessarily the computer running the ScanFish III Flight software. It just needs to be connected to the same LAN as the ScanFish III.

Two Digi boards (port and starboard) are present inside a ScanFish, each with its own individual IP address. Digi board is a generic name for a serial port card that is used to add the serial ports. In SF system it is used to expand a terminal server (Port Server TS), on SF tow end it connects the 4 serial ports (Port Server TS 4) on the Stbd bottle and 2 serial ports (Port Server TS 2) on the Port bottle while on its top side it connects through a network interface card (NIC)] to our LAN through a modem.

Note: With a Terminal server each terminal does not need its own network interface card and a modem and the connection resources are shared dynamically.

Standard practice is to assign numbers to the magnetometers from Port to Starboard. The operator can chose among the various virtual com ports numbers on the terminal server. The Digi RealPort Setup Wizard auto detects the IP address of both Digi boards on a ScanFish.

The SF bottle has its own preset IP address. If required to be changed, note the IP addresses of the Digi boards on the new Scanfish and enter the same into a Web browser. The username is ‘root’, and the password is ‘dbps’ to access the PortServer TS4/2 ME1 Configuration. 

Also for each port \ Advanced Serial Settings \ Allow multiple systems to simultaneously connect. Allow a minimum of 2 connections (for MagLog and QINSy PC simultaneously). Set ‘Control’ to ‘Shared’. 

Yet another example: The Port SF magnetometers 1 and 2 (Com 201 & 202) can be on the Port Digi board (10.10.103.105), and port SF magnetometers 3 and 4 (Com 205 & 206) on the starboard Digi board (10.10.103.106). Likewise Stbd. SF magnetometers 1 and 2 (Com 101 &102) on the Stbd. Digi board (10.10.103.101), and port SF magnetometers 3 and 4 (Com 103 & 104) on the starboard Digi board (10.10.103.102). Both Digi boards communicate to MagLog computer (10.10.103.233).

Com ports are set up on the Mag Log computer through the Digi board Setup 64.exe emulator software. Likewise on each ScanFish TPUs its two Digi boards have to setup through the Digi board Setup 64.exe emulator software.

Note: Selected com ports have to match on both SF TPU and MagLog computers.

Again on the MagLog software \Input Devices Configuration the connected Input Devices has to be added. For each added G822 \ Properties \Analog Channel Calibration Setup \ Channel (Depth & Altimeter) \ Manual Calibration the Scale and Bias values have to be added. While recording MagLog data the Scale and Bios values are recorded along with other information in*.loginfo files.

An interesting note: The ScanFish computers are using two network cards. One is used for the local network 192.168.127.XXX while the other card 10.10.103.XXX is to communicate with ScanFish. However the ScanFish SNR, TPU SNR updates are available on 192.168.0.XXX.

As you note that while no network card is set the address range 192.168.0.XXX yet we can get the update. The key is the same Sub Net mask on the same LAN. No Default Gateways have been set. In case it is, that too has to match. 

The C class addresses are not routable to the internet; there is a configured routed path between the disparate IP networks that contains those host addresses. If you can ping the different IP, that’s it! 

If you can’t ping, turn off firewalls, anti-virus…Other useful commands are traceroute and route.

Data strings:

ScanFish heading input to QINSy is through driver Generic Network input (UDP) (EIVAScanfishHeading.ini) Port 5000. ScanFish motion input to QINSy is through driver Generic Network input (UDP) (EIVAScanfishMotion.ini) Port 5000.

ScanFish various setups:

Different setups are employed for ScanFish spread. Either you setup EIVA Flight for SF tow control and monitoring and MagLog for maggi data flow control, monitoring and logging or you may use EIVA to setup the connections through EIVA Acquisition employing DataMon and logging mags data in Survey software.

Reference Block diagram.

Deployment (a leaf from my experience): 

Employ prudence as every team develops its own practice of deployment for efficiency, safety and policies. Running more than one ScanFish is lot about pragmatic imagination, understanding tides, current and effect of vessel speed apart from acquaintance with its sensors and behavior.

The procedure of deployment and recovery would depend upon the water depth, current and tide, sea state, mobilization, deck space, height of deployment frame and personnel available.

As the survey teams are getting better trained with hands on experience on ScanFish, deployment of a single SF is rather an easy task.

While the SF is hoisted on the A Frame, first the corner two maggies are simultaneously deployed in water by two survey crews then to inner ones keeping the balance of the ScanFish and the SF if finally lowered to the sea surface.

The other way is deploying the mags while moving the SF perpendicularly on the stern till all mags are deployed, so while one person deploys the mags, other holds the SF pole to keep it perpendicular for smooth deployment.

Due care has to be taken while deploying and running two SFs or more as the risk exponentially increases.

While deploying two scan fish the side scan is towed on the middle pulley and tow layback remains closest to vessel (at max. side scan layback of 200m in 50m depth, the Port SF is at 230m and stbd. SF is at 275m layback. Thus, maintaining a minimum 30m separation. 

During deployment, the farthest off SF is lowered first and put on surface mode while paying out, once it is out of visible range of >100m it is placed to a fixed depth of a few meters below water level. The nearer ScanFish (Port SF) is then lowered and payed out to about 50m layback and placed at fixed depth of few meters below water level. Finally SSS is lowered and kept close until the layback of both ScanFish is appropriate (approx. four times of water depth with a layback difference of about 30 meters between the two SFs). 

The other way is to deploy the shorter layback SF first after is at a fixed depth of a 15 -20m deploy the other SF and place it at a fixed depth of 2-5m and let it get past over on the side of the earlier deployed shorter distance SF.

The turns are always to the side of SF with the max. layback keeping a radius more than the max. layback.

Dependent on the direction of turn, for instance for a Stbd. turn, the Stbd. Scanfish is the farthest and Port SF and parked at the highest altitude (lowest depth) dependent on water depth approx... 30% of water depth and maintain due separation from the Port ScanFish towed in between the SSS and the stbd. SF being parked at a lower altitude (higher depth) throughout the turn. 

Bear in mind the position of the SSS and ensure it’s always the nearest tow. It’s prudent to bring the SSS as close as possible to prevent entanglement of the tow cables.

For example: with a water depth of >50m, the SSS Tow fish is at 15 -25 m the Port SF at 30 m and stbd. SF at 12.5 m depth.

In case the vessel speed lowers or there is a sharp turn the SF may not maintain its altitude and begin its fall. Also watch the speed; especially in the transition between going into the current with WSP 5 kts. If the SF pitch increases greater than 20° (constantly) or if flaps are on maximum (40°) SF may fail to maintain its altitude, increase vessel speed and if necessary winch in for the SF fins to be in control for maintaining altitude.

Run line begins 1000m from the SOL. First lowest layback SSS tow fish goes down then the highest layback SF is lowered and usually kept a little higher than the nearer SF in follow seabed mode.

Note: Farthest SF is lowered only after observing the horizontal separation (Beacons comparison) of both SF (to avoid snag risk). Usually snag risk is when we are running line along the tide/ current.

In case the apartness is less than 2 m (effect of current/tide), try increasing vessel speed. Lower SF by increasing the parking depth instead of Follow seabed mode while observing the apartness. It's always better to lower the parking depth in steps as sometimes the altimeter may not get the depth due to high pitch while lowering or hoisting.

After EOL hoisting procedure is the inverse - farthest SF comes up first, thereafter comes up the nearer layback SF and finally the SSS tow fish.

Sometimes altimeter won't see the bottom because of higher tile angle (more likely during turns) & it will panic surface. Once surfaced, its altimeter will again see the seabed and it will again dive to parking depths. Be observant!

Deployment of ScanFish from center of A Frame while towing from the ship side(s).

This is usually the scenario when the pulleys are on a low height (or Magnetometers toe cables are 10m long). It is also a good option to have 5m of maggi tow cables for ease of deployment and recovery.

SF is secured with locking or quick release shackles to both the winches cable end i.e. the center deployment winch and its side tow point SF winch. SF is pulled towards the center edge manually and the mags are dropped in water, outer first. SF is then hoisted on the A frame with a warn winch to shoulder level and A frame is moved out so the other two mags can be dropped in water. Once all 4 mags are out at least partially in water the check free swinging of SF, the center deployment winch cable is released while the SF winch gradually takes its weight moving it towards its tow position on the side pulley.

The center winch cable is now released by opening the locking shackle or the quick release shackle (Quick release shackle won't release with under load). Now the second SF is ready to be lowered....

Note: ScanFish has been quite an interesting & intriguing system to me personally and though all effort have been placed to bring forth a concise text, please employ prudence while referring these notes as this is a compilation of my experience on ScanFish surveys. In case of any incongruences or if you wish to share your observations and experience on ScanFish, feel free to comment or write to me at [email protected]

There's obviously more to it concerning operations, trouble shooting, maintenance and the most interesting 3D SF maneuvering. As time permits, I'll be updating!